The objective of this research is to determine whether significant advantages can be achieved in internal fixation plates of diaphyseal fractures through the use of internal fixation devices of improved design. We wish to test a hypothesis that internal fixation of plates of reduced axial stiffness are superior with respect to the late complication of stress protection induced osteopenia usually observed with traditional management. We have shown advantages to exist with respect to biomechanical properties of canine radii and femora internally fixed with plates that have large reduction in bending and axial stiffness. These results were confirmed by quantitative histological and biochemical measurements. Early vs. late plate removal is a controversial question. The second objective of this proposal is to study the effects of plate stiffness on the strength of fracture repair in order to withstand physiological loads. The hypothesis to be tested here is that early plate removal will prevent stress bypass osteopenia and facilitate more normal bone remodeling. Techniques to be used in this study include periodic x-rays to evaluate fracture healing in the plated canine femoral midshaft osteotomies. Nondestructive and destructive bioengineering tests, quantitative histological measurements using UV light microscopy to evaluate tetracycline labeling and microradiography and biochemical analysis of organic and inorganic matrix of bone will be used to evaluate the influence of the different internal fixation devices employed.